An OTN (optical transport network), as a core technology of a next-generation transport network, includes electrical layer and optical layer technical specifications, has rich OAM (operation, administration and maintenance) functions, a strong TCM (tandem connection monitoring) capability, and an outband FEC (forward error correction) capability, and can implement flexible scheduling and management of a large-capacity service.
An existing OTN system has four fixed line rates OTUk (optical channel transport unit, where k=1, 2, 3, 4 which correspond to rate levels of 2.5 G, 10 G, 40 G, 100 G respectively), and a service can be adapted into only the four fixed line rates OTUk. For example, at a site A, a 40 GE four-channel parallel signal needs to be aggregated with a 10 GE signal, and transmitted to a site B. In this case, an OTU4/ODU4 may be selected to perform aggregation. The 40 GE four-channel parallel signal is first converted into a serial 64B/66 B code stream, and is mapped to an LO ODU3 after being processed, and then is mapped to 31 timeslots of an HO ODU4; for the 10 GE signal, the 10 GE signal is first mapped to an ODU2e, and then is mapped to 8 timeslots of the HO ODU4; after a supervisory overhead is added to the HO ODU4, an OTU4 frame is formed. Generally, the OTU4 uses a low-cost OTL4.n (n=4, 10) multichannel parallel interface, and therefore the OTU4 needs to be further distributed to form the OTL4.n interface, and then the OTL4.n is modulated onto an optical carrier for transmission.
However, on one hand, with a great increase in upper-layer IP services, currently a beyond 100 G technology, for example, a 400 G or 1 T optical transport technology with higher spectral efficiency, is researched in the industry. In order to achieve an optimized and most efficient network configuration to improve efficiency of using optical spectrum resources, a Flex Grid technology is introduced to the optical layer to expand the spectrum from a conventional fixed 50 GHz spectral grid (ITU-T G.694) to a flexible spectral grid with a smaller granularity, where slot=12.5 GHz (a central frequency is 193.1 THz+n×slot/2, and spectral bandwidth is m×slot). In this way, a signal may occupy multiple consecutive spectral grids.
Changing a modulation format, a carrier symbol rate, and the number of multiple subcarriers implements that spectral bandwidth changes flexibly, thereby improving effective utilization of the spectrum resources and improving bandwidth usage. On the other hand, in terms of client services, with a rapid growth of data services, an increasing amount of information is encapsulated by using an Ethernet, FC (fiber channel), and ESCON (enterprise system connection) technology, and the number of rate levels is increasing. In order to flexibly support the data services, the OTN is additionally provided with ODUflex (optical channel data unit flex) to adapt data services with various bandwidth requirements. However, the line rates of the OTN still use fixed bandwidths of 2.5 G, 10 G, 40 G, and 100 G, which is not beneficial to more efficient use of transmission bandwidth. In addition, an increasing number of client signals use a multi-wavelength parallel interface, for example, a 100 GE multichannel parallel interface, to replace the conventional serial interface, so as to implement low-cost access of a high-speed service. At the present, in order to adapt a client signal of a multi-wavelength parallel interface into a parallel OTN interface, a manner of “multiplexing, distribution, and multiplexing” is still used, and therefore processing is quite complex.
As described above, in a process in which a client signal and optical layer spectral bandwidth evolve to higher-rate ones, both the client signal and the optical layer technology have a trend of flexibility and parallelization. Therefore, it is a to-be-resolved problem that how the transport network evolves to further simplify a service processing process, thereby improving bandwidth usage and reducing network complexity, so as to adapt to a variation trend of the client signal and the optical layer spectral bandwidth.